1. Field of the Invention
The present invention relates to an automatic transmission in which respective elements of first and second multiple planetary gear sets can be coupled to an input shaft via a clutch and can be fixed via a brake, so as to shift rotation of the input shaft with plural speeds and transfer the rotation to an output shaft.
2. Description of the Related Art
In Japanese Patent Application Publication No. JP-A-2002-213545 (p. 8, FIG. 4), there is described an automatic transmission, in which an input shaft, a first multiple planetary gear set, a second multiple planetary gear set, and an output shaft are arranged on a common axis in a transmission case, and respective elements of first and second multiple planetary gear sets are coupled to the input shaft selectively via a clutch and fixed selectively via a brake, thereby shifting rotation of the input shaft with eight forward speeds and a reverse speed and transferring the rotation to the output shaft. Then in the automatic transmission shown in FIG. 4 of Japanese Patent Application Publication No. JP-A-2002-213545, the first multiple planetary gear set 60 is structured including a common sun gear S1S2 coupled to an input shaft 15, a common carrier C1C2 which supports a long pinion 63 meshing with the common sun gear S1S2 and a pinion 64 meshing with the long pinion 63 and can be fixed via a second brake B-2, a first ring gear R1 which meshes with the long pinion 63 and can be fixed via a first brake B-1, and a second ring gear R2 which meshes with the pinion 64 and can be fixed via a third brake B-3. The second multiple planetary gear set 17 is structured including directly coupled third and fourth sun gears S3, S4 which can be coupled to the input shaft 15 via a first clutch C-1, third and fourth ring gears R3, R4 which mesh with the third and fourth sun gears S3, S4 via pinions 33, 34 and can be fixed respectively via the third and fourth brakes B-3, B-4, a third carrier C-3 which supports the pinion 33 and can be coupled to the input shaft 15 via a second clutch C-2, and a fourth carrier C-4 supporting the pinion 34 and coupled to an output shaft 18.
In FIG. 4 of Japanese Patent Application Publication No. JP-A-2002-213545, the first and second clutches are arranged inside a coupling portion of the common ring gear R2 of the first multiple planetary gear set and the third ring gear R3 of the second multiple planetary gear set. However, providing two clutches inside a rotating member results in a complicated structure and causes a problem of increase in size.
Further, in paragraphs [0040] [0041] of Japanese Patent Application Publication No. JP-A-2002-213545, it is also described that a large relative rotation difference occurs between the ring gears and the sun gear of the first multiple planetary gear in the first forward speed and results in fast autorotation of the pinions meshing with the both, and accordingly, to prevent this autorotation, a new clutch can be interposed between the common sun gear and the input shaft so as to allow selective coupling. However, when the new clutch is interposed between the common sun gear and the input shaft in FIG. 4 of Japanese Patent Application Publication No. JP-A-2002-213545, the size of the automatic transmission in a radial direction becomes quite large.